Tertiary diamide lubricants

ABSTRACT

NOVEL SYNTHETIC LUBRICANTS CONTAINING A MAJOR AMOUNT OF TERTIARY DIAMIDES HAVING THE FOLLOWING STRUCTURAL FORMULA:   R-CO-N(-CH3)-CH2-C(-CH3)2-(CH2)N-C(-CH3)2-CH2-N(-CH3)-CO-R   WHEREIN N= 0-10 R=-(CH2)M-CH3 WHEREIN M= 4-12 ARE DISCLOSED. THERE LUBRICANTS HAVE LOW POUR POINTS AND POSITIVE VISCOSITY INDEXES.

United States Patent 3,827,981 TERTIARY DIAMIDE LUBRICANTS Robert M. Thompson, Wilmington, Del., assignor to Sun Research and Development Co., Philadelphia, Pa. No Drawing. Filed Oct. 2, 1972, Ser. No. 293,982 Int. Cl. Cm 3/30 U.S. Cl 252-515 A 9 Claims ABSTRACT OF THE DISCLOSURE Novel synthetic lubricants containing a major amount of tertiary diamides having the following structural formula:

are disclosed. These lubricants have low pour points and positive viscosity indexes.

CROSS-REFERENCES TO RELATED APPLICATIONS This invention is related to those described in the following listed applications:

All of the aforementioned applications filed the same date as this application. The first and second of the aforementioned applications relate to a class of novel diamides; the third to the use of certain tertiary diamides as swelling agents; the fourth to the use of certain tertiary diamides in greases and the last one to the use of certain tertiary diamides as lubricants.

SUMMARY OF THE INVENTION This invention pertains to novel synthetic lubricants containing a major amount of tertiary diamides having the formula:

and a minor amount of lubrication additives. These liquid lubricants have low pour points despite their high kinematic viscosities and high boiling points. This invention also relates to a method of lubrication.

BACKGROUND OF THE INVENTION Stringent and specific lubrication requirements of modern technology, such as high thermal and oxidative stability and suitable physical properties over a wide temperature range; have spurred on the development of new synthetic lubricants having a particular advantage in that their physical properties can be regulated by the proper "ice choice of structure. A wide number of synthetic lubricants have found acceptance in industrial and military application. A comprehensive discussion of these synthetic lubricants and their application is given in Kirk-Othmer, Encyclopedia of Chemical Technology, 2nd Edition, Volume 12. In addition, US. Pat. 3,312,620, H. Low and I. E. Lauck, Apr. 4, 1967, relates to the use of certain N,N-disubstituted amides as synthetic lubricant base stocks. However, the aforementioned lubricants cannot satisfy all the needs of modern technology, particularly where there is a need for high boiling point lubricants having a high kinematic viscosity and a low pour point.

DESCRIPTION OF THE INVENTION It has now been discovered that certain tertiary diamides are efiective lubricant base stocks. These diamides have the following structural formula:

Representative tertiary diamides of the invention are N, N'-2,2,5,5-tetramethylhexamethylene-N,N' dimethylpelargonarnide, N,N-2,2,6,6-tetramethylheptamethylene N, N-dimethylpelargonamide, N,N' 2,2,6,6 tetramethylheptamethylene-N,N'-dimethylsebacamide.

The tertiary diamides of this invention can be prepared by the methylation of a sodium salt of a suitable diamide by using, for example, methyliodide. This general reaction is illustrated by the following equation:

CH; CH;

CH: CH: H H H H RC-NC (CH3),, C-N-CR g H l H ll CH: CH: The R of the saturated aliphatic nonacid of equation 1 equals (CH ),,,CH wherein m=4-12, preferably, 5- 10 while the n of the diamine equals 0-10, preferably, 1-8.

Precursors of the suitable diamines of equation (2) can be prepared by hydrogenating a suitable nitrile. A suitable nitrile is a parafiinic aliphatic material having 3 two methyl radicals attached to each of the two ,6 carbons. This general reaction is illustrated by the following equation:

(s H. CH:

NEG--(Cfizh- CEN H:

CH: CH:

CH; CH:

H H=N%-(h-(CH,).. o-NH, H l I H CH: CH3 The n of the nitrile of equation (3) equals 0-10, preferably, 1-8.

The precursors of the nitriles of equation 3) can be prepared by interaction of a suitable paraffimc dihahde with sodium or potassium cyanide in aqueous-alcoholic solution, thus The R of the paraffinic halide equals wherein n equals 0-10, preferably, 1-8.

Particular nitriles can be prepared by other methods than that shown by equation (4). For example, 2,25,5- tetramethylhexamethylene dinitrile can be prepared by the free radical coupling of pivalonitrile ((CH3)3CCEN).

The present invention contemplates the use of these compounds and mixtures thereof as base lubricants; i.e., a major proportion (at least half) of the lubricant comprises the above defined tertiary diamides. It is preferred that amides of the invention comprise at least 75%, preferably at least 90% by weight of the final lubricant composition. The balance of the lubricant contains minor amounts of additives. These additives include oxidation inhibitors, rust inhibitors, antiwear agents, detergent-dispersants and foam inhibitors. These additives are described in Kirk-Othmer, Encyclopedia of Chemical Technology, 2nd Edition, Volume 12, Lubrication and Lubricants.

The present invention is partly based on the discovery that the tertiary diamides of present invention have, compared to N,N'-disubstituted amides such as N,N-di-n-propylbenzamide, low pour points despite their high boiling points and high kinematic viscosities, particularly at 100 F. Furthermore, the tertiary diamides have high positive viscosity indexes compared to the negative viscosity indexes for the disubstituted aromatic amides. These differences are apparent from a comparison of the data relating to a tertiary diamide of present invention and a disubstitutecl aromatic amide shown in the accompanying Table I.

TABLE L-LUBRICATING PROPERTIES OF CERTAIN AMIDE FLUIDS Also, the present invention is partly based on the tertiary amides unique combination of kinematic viscosity and pour point compared to the same properties of petroleum lubricating oils and synthetic oils. Thus, for example, as shown in the accompanying Table II, petroleum lubricating oils (SAE 30 and 40) bracket the kinematic viscosity at 100 F. of a tertiary diamide, yet the petroleum oils have pour points of 0 F. whereas a diamide has a much lower pour point; i.e., 45 P.

On the other hand, while a synthetic oil has a much lower pour point than a tertiary diamide, e.g. F. versus 45 F., respectively, the diamide has a higher kinematic viscosity at P. which can meet unique mdustrial lubricating requirements.

The lubricants of present invention can be used Wherever it is desirable to separate moving surfaces to minimize friction and wear. In particular, the lubricants, because of their extremely high boiling points, are useful in high temperature environments and yet, because of their low pour points, can also be used in a low temperature environment. Engines, particularly internal combustion engines, e.g. gasoline engines, are exposed to such low-high temperature environments.

Following is an example of how a tertiary diamide of present invention was prepared; also reported is its physical properties.

EXAMPLE (a) Preparation of the dinitrile.0ne gram mole of pivalonitrile ((CH C-CEN) and 1300 milliliters of water were charged to a reaction vessel. While the contents of the vessel were agitated, milliliters of 6.67 molar hydrogen peroxide solution and 750 milliliters of 1.33 molar ferrous sulfate solution were added simultaneously and equivalently from calibrated burets. The ferrous sulfate solution was prepared from 278 grams of ferrous sulfate heptahydrate, 55 milliliters of sulfuric acid and 575 milliliters of water. During the simultaneous addition, which required some fifteen minutes, the agitated mixture was maintained at a temperature of 30 C. by means of an ice-bath. Afterwards, the solid dinitrile was removed from the mixture by filtration. The removed solid dinitrile was water washed and dried. The dried dinitrile was recrystallized from milliliters of ethyl alcohol. The recrystallized a,11,41,a'-tetramethyladiponitrile had a melting point of l37l38 C.

(b) Preparation of the diamilze.-50 grams of the aforementioned dinitrile were charged to a one liter bomb along with 500 milliliters of methanol and 5 grams of Raney nickel. Also, the bomb was pressurized with hydrogen to a pressure of 1200 p.s.i.g. The bomb with its contents was heated to a temperature of 60 C. and rocked for 8.5 hours. Then, after the temperature of the bomb reached ambient temperature, the bomb was opened and the reaction mixture removed. The latter was filtered to remove the Raney nickel and subsequently, the methanol evaporated. The remaining viscous oil 'Was distilled. Its boiling point was 60 C. at 4 mm. Hg. The measured nitrogen content of the 2,2,5,5-tetramethylhexamethylene drarnine was 15.9 weight percent compared to 16.3 weight percent calculated for C H N (0) Preparation of the pelargonamide.0.116 moles (20 grams) of the previously mentioned diarnine and 0.116 moles (36.8 grams) of pelargonic acid (CH (CH2)7COOH) were charged to a 200 milliliter, 3-neck flask equipped with a magnetic stirring bar, thermometer and Dean Stark trap and condenser. The resulting mixture in the flask was heated to a temperature of ISO- C., with stirring, and maintained at that temperature until no more water, a reaction product, came over into the Dean Stark trap.

Afterwards, the heating was stopped, the flask and its contents were allowed to cool. After cooling, 150 milliliters of other were added to the contents in the flask, and then the ether solution was first washed with a dilute HCl solution, then washed with a 5% aqueous Na CO solution and finally washed with just water. Any water in the other solution was removed by contacting the solution with MgSO Afterwards the ether was removed by application of a vacuum. The resulting white solid pelargonamide, 45 grams, had a melting point of 77-79 C (d) Methylation of the pelargonamide.800 milliliters of sodium dried xylene were charged to a 2 liter reaction flask equipped with stirrer, reflux condenser and nitrogen inlet. The xylene had been just recently distilled to remove impurities. Also, to the reaction flask were charged 3.5 grams of sodium and 33 grams of the aforementioned pelargonamide. The resulting mixture in the flask was agitated and refluxed overnight under a nitrogen atmosphere.

After refluxing overnight, the three component mixture was transferred under nitrogen to a dry one liter flask equipped with a cold finger condenser, magnetic stirrer and nitrogen inlet. The cold finger condenser contained a Dry-Ice-acetone mixture. The flask was heated to a temperature of 40 C. and while maintained at that temperature, 17.7 grams of methyl iodide were added to the agitated mixture dropwise. The dropwise addition was completed in an hour, but the agitation at room temperature, continued for about 20 hours. The flask and its contents were allowed to cool; afterwards the mixture was filtered to remove the precipitated sodium iodide. The filtered solution was water washed and the xylene solvent removed by distillation. Infrared examination of the resulting 25 grams of liquid indicated the presence of NH bands and therefore, that the reaction was incomplete.

The aforementioned procedure for the methylation of the pelargonamide (step d) was repeated. After this second treatment, the amide liquid, as indicated by infrared examination, was free of NH bands. The color of the resulting N,N dimethyl-2,2,5,5-tetramethylhexamethylene-N,N-dimethylpelargonamide was slightly yellow. Its kinematic viscosity at 100 F. was 148.6- cs.; at 210 F. it was 12.11 and had a 45 F. pour point.

TABLE II.-VISCOSITY AND POUR POINT COMPARISON OF SEVERAL LUBRICATING OILS AND TERTIARY The invention claimed is:

1. A lubricant composition comprising a major amount of at least one tertiary diamide having the formula:

CH3 CH3 CH3 CH3 RCI ICHz C- (CH1) n CH3-I I CR CH, OH: I

wherein wherein m=4-12 and a minor amount of lubrication additive.

2. Composition according to Claim 1 wherein n=1-8 and m=5-10.

3. Composition according to Claim 2 wherein the diamide is N,N' 2,2,5,5-tetramethylhexamethylene-N,N'- dimethylpelargonamide.

4. A method of lubrication which comprises maintaining next to the surface to be lubricated, a film of lubricant containing a major amount of at least one tertiary diamide having the formula:

7. Method according to Claim 5 wherein the surface I to be lubricated is a surface related to an internal combustion engine.

8. Method according to Claim 7 wherein the internal combustion engine is a gasoline engine.

9. Method according to Claim 8 wherein the diamide is N,N'-2,2,5,5-tetramethylliexamethylene-N,N-dimethylpelargonamide.

References Cited UNITED STATES PATENTS 3,312,620 4/1967 Low et al 25251.5 A 2,710,839 6/1955 SevakOn et al. 252S1.5 A

DANIEL E. WYMAN, Primary Examiner I. VAUGHN, Assistant Examiner 

